(a) Field of the Invention
The present invention relates to an iron golf club, specifically to a head structure thereof.
(b) Description of Prior Art
Typically, iron golf clubs have two types, i.e., muscle back type and cavity back type. A head of cavity back type is formed with a cavity provided at a back side of a head body having a striking face, while a head of muscle back type, which is more conventional than the former, is free of such a noticeable concave as that of the cavity back type.
With a head of muscle back type, you can obtain a sharp feeling in striking balls, and strong balls can be struck using this type of head. The "strong balls" is meant here as balls that travel comparatively straight, without being influenced by the wind, due for example to good spins of balls. On the other hand, such muscle back type head has a drawback such that it has a comparatively small sweet area or an area on a face within which a ball travels well when struck thereon. In contrast, a head of cavity back type has advantages such that owing to its cavity, its face can be enlarged without making the total weight of the head heavier, and the weight can be distributed toward the peripheral portion thereof so that a moment of inertia of the head is enlarged so as to enlarge a sweet area. In other words, if you strike a ball at a position away from the foot of a perpendicular line from the center of gravity of the head to the face, the deflection of the head would be lessened, thus decreasing so-called mis-shots. With the cavity back type, however, so-called "striking core" would be made unclear when striking balls, thus leading to an inferior feeling in striking.
In Japanese Patent Application Un-Examined Publication No.8-38657, there is proposed a golf club head which is an intermediate type between the muscle back type and the cavity back type, which comprises a recess formed at the back side of a head body, and a balance weight fitted into said recess, said balance weight being made of a material having the smaller specific gravity than that of the head body. According to such conventional structure, a good feeling in striking balls relatively close to that of the muscle back type is able to be obtained, with the effect of the weight distribution toward the periphery being ensured to some extent. However, the head according to the above No.8-38657 publication has a material of comparatively large specific gravity located at its face side, while another material of comparatively small specific gravity located at its back side, so that so-called the depth of the center of gravity (or a distance from the face to the center of gravity of the whole head) is made comparatively small. Whilst the deepening of the center of gravity as well as the suitable weight distribution toward the periphery of the head is generally recognized as means for enlarging a sweet area, the conventional head of the No.8-38657 publication has such a small depth of the center of gravity that a sweet area also is narrowed comparatively.
Referring to another prior art described in Japanese Patent Application Un-Examined Publication No.9-24125, it discloses, although an object of its invention is somewhat different, an iron golf club head comprising a head body with a recess formed at the back thereof, a rubber-like elastic body fitted into said recess and a cover (rear face member) which covers the elastic body and is fixed thereto by screws. According to this conventional head, the specific gravity of a material of the cover is greater than that of a material of the head body in order to enlarge a sweet area. The prior head has indeed an advantage that the struck balls are able to travel a longer distance owing to the elasticity of the rubber-like elastic member. However, you cannot obtain so good a feeling in striking balls as the muscle back type head, since the member provided at the rear side of the face is no more than a rubber-like elastic body. In addition, as the head described in No.9-24125 publication has the cover fixed by screws, the attractiveness of the head would be impaired.
Incidentally, welding, for example, can be thought of as means for fixing the cover to the head body. With the welding, however, there would remain welding marks and /or pin holes, and thus it also impairs the attractiveness of the head. Further, as welding is sometimes impossible, depending on the materials of the head body and/or the cover, the selection of the materials would be restricted. In addition, in the case of plating, some metallic materials indicate inferior adherence in plating.